That makes it completely impossible to advance at all. There is no reason for the rules even to be there.
Neil's understanding (and apparent intention), that the capacity of an immortal's talisman should be unlimited, makes things significantly different than I had thought with my one xp per level missreading. I think more interesting too.
My reading allows the immortal (assuming scores of thirty) 600 xp in an empty talisman (perhaps half that much if the talisman already has some effects in it) and forcing them to make that alotment last them the rest of eternity but they have the option to gain that xp at a rate of about 1/2 as fast as a living magus (one season study, one season enchantment).
Neil's idea lets the imortal learn as much as they like but at a snails pace (making it very much like guardian of nature) learn one season, then enchant a level 40 effect the next season to give you an advancement average of 2 xp per season.
To make Neil's intention work there will have to be a house rule or errata to the effect of "enchantments in a talisman to fix experience gain do not count towards filling the capacity of the talisman".
Of course another option for the immortal could be this,
forum.atlas-games.com/viewtopic. ... a2683b1bee